You can swallow, but just getting a really wet mouth is a sign you're not in the proper brain state to WILD.

2. I close my eyes and try to focus on the phospenes but i just can't see anything.

If you have not experienced many hypnagogic images spontaneously and learned to induce them intentionally one likely can't do do a WILD. You might still be able to do demi-WILDs such as dream returns and the wake back to bed kind.

3. I relax for 15-20 min but nothing ever happens, i just get this weird feeling like a heavy weight was put on my chest.

The heavy weight is either self hypnosis or an incubated HI.

I experienced WILDs spontaneously and taught myself to do them intentionally by just putting my brain in the same state it was in when they occurred.

"There is only one God and his name is Death.And there is only one thing we say to death "not today"- Syrio Forel